Engine starting apparatus for cranking internal combustion engines can utilize a starter drive that has an over-running clutch. During engine cranking, the over-running clutch is driven by an electric cranking motor and the clutch drives a pinion that, in turn, drives the ring gear of an engine. When the engine starts, the clutch over-runs to thereby prevent the running engine from driving the electric cranking motor.
Engine starting apparatus that utilizes an over-running clutch can produce cranking noise particularly where the pinion is driven from the cranking motor through a gear speed reduction drive. The noise produced is impulsive and is the result of mechanical impact in the starter driveline to the engine. During engine cranking, the load torque due to the engine varies as the engine cylinders go through their compression or expansion strokes. Each time a cylinder begins its compression stroke, it creates a negative engine torque which tends to slow down the engine crankshaft and flywheel. As the piston in a cylinder travels through top dead center, it creates a positive torque which accelerates the flywheel. Due to the large effective inertia of the motor drive (the effective inertia is proportional to the square of the drive ratio), the cranking motor speed cannot follow the engine speed. Therefore, the engine overruns the over-running clutch until the next cylinder begins its compression stroke. This repetitive engaging and disengaging of the over-running clutch creates a noise producing mechanical impact.